A test shall be used on pipe using which gas or condition?

• A. Oxygen at elevated pressure
• B. Argon under high vacuum
• C. Nitrogen or dry air not exceeding normal operating pressure
• D. Helium at high pressure

Answer: (C)

When testing a pipe with gas, you want a medium that won’t react, ignite any residues, or cause corrosion, and you want to test under the pressures the system will actually see in service. Nitrogen is inert, and dry air minimizes moisture, so both are safe and practical choices for leak testing. Importantly, you test at not more than the normal operating pressure so you’re simulating real conditions without over-stressing the piping.

Using oxygen at elevated pressure introduces a significant fire and explosion risk if any oils or residues are present, which makes it unsuitable. Argon under high vacuum doesn’t reflect the typical service environment and is impractical for standard leak checks. Helium at high pressure can be expensive and also pushes the system beyond normal operating conditions, which isn’t necessary for a standard integrity test.